Multilayer structured coatings for cutting tools

ABSTRACT

Cutting tools are described having coatings which can demonstrate desirable wear resistance and increased cutting lifetimes. A coated cutting tool described herein has a substrate and a coating with a plurality of alternating layers of a first layer of Al 2 O 3  and a second layer of at least one of MeAl 2 O 3  and MeAl 2 O 3 /MeO 2  composite, wherein Me is Zr, Hf, Ti or a combination thereof. The coating has a superlattice-like structure.

FIELD

The present invention relates to coatings for cutting tools and, in particular, to coatings deposited by chemical vapor deposition (CVD).

BACKGROUND

Cutting tools, including cemented carbide cutting tools, have been used in both coated and uncoated conditions for machining various metals and alloys. In order to increase cutting tool wear resistance, performance and lifetime, one or more layers of refractory material have been applied to cutting tool surfaces. TiC, TiCN, TiN and/or Al₂O₃, for example, have been applied to cemented carbide substrates by CVD and by physical vapor deposition (PVD). While effective in inhibiting wear and extending tool lifetime in a variety of applications, refractory coatings based on single or multi-layer constructions of the foregoing refractory materials naturally have performance limits, thereby calling for the development of new coatings with improved properties.

SUMMARY

In one aspect, cutting tools are described having coatings adhered thereto which, in some embodiments, can demonstrate desirable wear resistance and increased cutting lifetimes. A coated cutting tool described herein comprises a substrate and a coating comprising a plurality of alternating layers comprising a first layer of Al₂O₃ and a second layer of at least one of MeAl₂O₃ and MeAl₂O₃/MeO₂ composite, wherein Me is Zr, Hf or Ti or a combination thereof.

Methods of making coated cutting tools are also provided. A method of making a coated cutting tool described herein comprises providing a cutting tool substrate, and depositing over a surface of the cutting tool substrate by CVD a coating comprising a plurality of alternating layers comprising a first layer of Al₂O₃ and a second layer of at least one of MeAl₂O₃ and MeAl₂O₃/MeO₂ composite, wherein Me is Zr, Hf, Ti or a combination thereof. The plurality of alternating layer may begin with the first or second layer nearest the substrate.

These and other embodiments are described in greater detail in the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a coated cutting tool according to one embodiment described herein.

FIG. 2 is a cross-sectional scanning electron microcopy (SEM) image of a coated cutting insert according to one embodiment described herein.

FIG. 3 is a magnified, cross-sectional scanning transmission electron microcopy (STEM) bright field (BF) image of a coated cutting insert according to one embodiment described herein.

FIG. 4 is the magnified, cross-sectional STEM BF image of a coated cutting insert according to one embodiment described herein from FIG. 3.

FIG. 5 is a magnified, cross-sectional STEM High Angle Annual Dark Field (HAADF) image of a coated cutting insert according to one embodiment described herein.

FIG. 6 is a magnified, cross-sectional STEM HAADF image of a coated cutting insert treated with a focused ion beam according to one embodiment described herein.

FIG. 7 is a schematic of various doping processes according embodiments described herein.

DETAILED DESCRIPTION

Embodiments described herein can be understood more readily by reference to the following detailed description and examples and their previous and following descriptions. Elements, apparatus and methods described herein, however, are not limited to the specific embodiments presented in the detailed description and examples. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those of skill in the art without departing from the spirit and scope of the invention.

I. Coated Cutting Tools

In one aspect, cutting tools are described having coatings adhered thereto which, in some embodiments, can demonstrate desirable wear resistance and increased cutting lifetimes. Referring now to FIG. 1, a coated cutting tool 10 described herein may comprise a cutting edge 12, a rake face 14, a flank face 16 and a mounting hole 18. The insert 10 may be a variety of geometries and configurations, e.g. with or without chipbreakers, mounting hole or positive or negative rake angle.

Referring now to FIG. 2, one embodiment described herein provides a cutting insert 20. The cutting insert 20 has a substrate 22 and a coating adhered to the substrate 22, the coating has a multilayer structure comprising an optional inner layer 24 and an optional bonding layer between the inner layer 24, a superlattice-like coating 26 and outmost coating layer 28. The super-lattice like coating comprises repeating coating layers designated A and B wherein A and B represent a periodicity of dopant-containing Al₂O₃ (B) and un-doped Al₂O₃ (A) sequences. Alternatively, the periodicity may include dopant-containing Al₂O₃ (B) and low level doped Al₂O₃ (A). Dopants may include Ti, Zr, Hf or a combination thereof. The alternating doping layer and un-doped layer or different doping level layers can induce the formation of superlattice-like coating structures.

In one embodiment of the present invention, the cutting insert 20 comprises a substrate 22. Substrates of coated cutting tools can comprise any material not inconsistent with the objectives of the present invention. In some embodiments, a substrate comprises cemented carbide, PCD, PcBN, ceramic, cermet or steel.

A cemented carbide substrate can comprise tungsten carbide (WC). WC can be present in a substrate in an amount of at least about 70 weight percent. In some embodiments, WC is present in a substrate in an amount of at least about 80 weight percent or in an amount of at least about 85 weight percent. Additionally, metallic binder of a cemented carbide substrate can comprise cobalt or cobalt alloy. Cobalt, for example, can be present in a cemented carbide substrate in an amount ranging from about 3 weight percent to about 15 weight percent. In some embodiments, cobalt is present in a cemented carbide substrate in an amount of 5-12 weight percent or 6-10 weight percent. Further, a cemented carbide substrate may exhibit a zone of binder enrichment beginning at and extending inwardly from the surface of the substrate.

Cemented carbide substrates can also comprise one or more additives such as, for example, one or more of the following elements and/or their compounds: titanium, niobium, vanadium, tantalum, chromium, zirconium and/or hafnium. In some embodiments, titanium, niobium, vanadium, tantalum, chromium, zirconium and/or hafnium form solid solution carbides with WC in the substrate. The substrate, in some embodiments, comprises one or more solid solution carbides in an amount ranging from about 0.1 weight percent to about 5 weight percent. Additionally, a cemented carbide substrate can comprise nitrogen.

In some embodiments, a substrate of a coated cutting tool described herein comprises one or more cutting edges formed at the juncture of a rake face and flank faces of the substrate. In some embodiments, a substrate of a coated cutting tool is a drill bit, end mill, saw blade or other cutting apparatus.

A coating adhered to the substrate may comprise a bonding layer between the inner layer 24 and the superlattice-like layer 26. A bonding layer comprises TiCN and TiAlOC. In some embodiments, a bonding layer further comprises TiOCN. TiCN, TiAlOC and TiOCN can be provided as sublayers of the bonding layer. Further, a bonding layer of structural unit generally has a thickness less than 5 μm. In some embodiments, a bonding layer has a thickness selected from Table I.

TABLE I Bonding layer thickness (nm) Bonding Layer Thickness (nm) 10-950  5-500  5-200 10-100 When one or more sublayers of TiCN, TiAlOC and/or TiOCN constitute a bonding layer, the sublayers can each have a thickness of 5-500 nm. In some other embodiments, a diffusion barrier layer comprising nitride, TiN, ZrN and HfN and/or their combination can adhere to the substrate directly. The thickness of the diffusion barrier can be less than 2 μm.

Further, a coating described herein can also comprise one or more outer layers over the structural units. An outer layer, in some embodiments, comprises one or more metallic elements selected from the group consisting of aluminum and metallic elements of Groups IVB, VB and VIB of the Periodic Table and one or more non-metallic elements selected from the group consisting of non-metallic elements of Groups IIIA, IVA, VA and VIA of the Periodic Table. In some embodiments, one or more outer layers deposited over the structural units comprise a nitride, carbonitride, oxide or boride of one or more metallic elements selected from the group consisting of aluminum and metallic elements of Groups IVB, VB and VIB of the Periodic Table. For example, one or more outer layers are selected from the group consisting of TiN, TiCN and TiOCN. Outer layers of coatings described herein can have any thickness not inconsistent with the objectives of the present invention. An outer layer of a coating, in some embodiments, can have a thickness ranging from 0.5 μm to 5 μm. With all components accounted for, a coating described herein can have a thickness up to 25 μm. A coating, for example, can have a total thickness of 2-15 μm or 5-20 μm.

FIG. 3 is a STEM-BF image of a cross-section of a coating 30 according to one embodiment of the present invention. The alternating A/B layers 32, 34 can be clearly seen in the image. An A-layer 32, with darker contrast in the image, represents a doped layer while a B-layer 34, with lighter contrast in the image, represents a layer having lesser or no doping. Alternating dark regions 36 and light regions 38 are visible at grain boundaries. The dark areas 36 indicate intergranular ZrO₂ deposits. Numerous ZrO₂ deposits distributed along the grain boundaries are visible in the image although dark area 36 is the only deposit specifically called out in FIG. 3.

FIG. 4 is also a STEM-BF (Bright Field) image of a cross-section of a coating 40 according to one embodiment of the present invention. The alternating A/B layers 42, 44 can be clearly seen in the image. An A-layer 42 represents a layer having lesser or no doping while a B-layer represents a doped layer. Alternating dark regions 46 and light regions 48 are visible at grain boundaries. The dark areas 46 indicate intergranular ZrO₂ deposits.

FIG. 5 is a STEM-HAADF (High Angle Annular Dark Field) image of a cross section of a coating 50. Dark layers 52 in the HAADF image indicate lack of dopant. Lighter layers 54 indicate higher levels of dopant. The light areas 56 indicate intergranular ZrO₂ deposits. FIGS. 3-5 show a unique chevron pattern present within the individual coating grains.

In one embodiment the present invention has an alternative doped alumina layer and un-doped alumina layer coating scheme or different doping levels with alternative high level and low level or different dopant multi-periodicity layers. It will be apparent to one skilled in the art that the periodicity pertains to high level and low level doping with Zr, Hf or Ti and the low level doped layers may have no dopant or a lesser amount of dopant than the high level dopant layers. As used herein the “low doped layer” and “high doped layer” refer to the alternating alumina containing layers where the high doped layer contains more dopant than the low doped layer and the low doped layer less dopant than the high doped layer or no dopant at all. The coating scheme includes CVD coating layers involving alternating high doped layers and low doped layers having pre-defined layer thickness and/or grain size. The alternative high doped layer and low doped layer along with nano-scale layer thickness induces the formation of superlattice-like structures. The multilayer coating scheme layer thickness and/or crystal grain size can be tuned in the range from 0.5-20 microns by adjusting the process duration designed for the different coating layers and dopant and alumina source ratios. The individual high doped and low doped layers may both be in the range of 0.050-0.2 microns. Different phases of alpha and kappa alumina may be introduced into the coating scheme by alternate the bonding and interlayer structures. The coating procedure provides great opportunity to control the doping level with well-designed dopant introduction. The alumina dopants can be ZrCl₄, HfCl₄ or TiCl₄ generated by reaction between HCl gas with metal species of Ti, Zr or Hf mixtures at 360˜450° C. The innovative coating procedures also provide great opportunity to manipulate the coating structure. Doped grain size can be controlled, especially, zirconium doped alumina (ZrAl₂O₃), with ZrO₂ formation in the coating system. This is due to the competition and selectivity between Al₂O₃, ZrO₂, doped alumina (ZrAl₂O₃) and the second phase ZrO₂ formation.

FIG. 6 is a cross section of a coating sample 60 according to one embodiment of the present invention. The sample was prepared by treating with a focused ion beam. Locations 62, 64 and 66 were analyzed using energy dispersive spectroscopy (EDS) in a STEM. Table II contains the quantitative data resulting from the EDS spectra for each of the locations 62, 64, 66.

TABLE II Quantitative EDS of a coating sample 60 Location Element Weight % Atomic % 62 O 39.92 58.67 Al 42.1 36.69 Zr 17.96 4.63 64 O 39.76 52.98 Al 59.19 46.76 Zr 1.03 0.24 66 O 46.24 59.20 Al 53.75 40.79 Zr 0.00 0.00

Location 62 is a composite portion of the coating containing high levels of Zr (17.96 weight %) due to the formation of an intragrain of ZrO₂. Location 64 is within a doped layer of the coating sample 60. Location 64 contains 1.03 weight % of Zr and 59.19 weight % of Al. Location 66 is within an un-doped layer of the coating sample 60. Location 66 contains no Zr and 53.75 weight % of Al.

A thin TiCN/TiN-top layer may be deposited for wear indication and optical appearance. The TiCN/TiN top layer can be also functioned as sacrificial layer for post coat wet-blasting or dry-blasting to modify the stress situation in the coating layers. Other outer layer systems, such as ZrCN, HfCN and TiOCN can be applied to coating scheme as well.

The coating scheme layer thickness can be tuned in the range from 0.05-20 microns by adjusting the process duration designed for the different coating layers and dopant and alumina source ratios.

Coatings of cutting tools described herein can be subjected to post-coat treatments. Coatings, for example, can be blasted with various wet and/or dry particle compositions. Post coat blasting can be administered in any desired manner. In some embodiments, post coat blasting comprises shot blasting or pressure blasting. Pressure blasting can be administered in a variety of forms including compressed air blasting, wet compressed air blasting, pressurized liquid blasting, wet blasting, pressurized liquid blasting and steam blasting. Wet blasting, for example, is accomplished using a slurry of inorganic and/or ceramic particles, such as alumina, and water. The alumina particle slurry can be pneumatically projected at a surface of the coated cutting tool body to impinge on the surface of the coating. The alumina particles can generally range in size between about 20 μm and about 100 μm.

Blasting parameters include pressure, angle of impingement, distance to the part surface and duration. In some embodiments, angle of impingement can range from about 5 degrees to about 90 degrees, i.e., the particles impinge the coating surface at an angle ranging from about 5 degrees to about 90 degrees. Suitable pressures can range from 30-55 pounds per square inch (psi) at a distance to the coated surface of 1-6 inches. Further, duration of the blasting can generally range from 1-10 seconds or longer. Blasting can be generally administered over the surface area of the coating or can be applied to select locations such as in a workpiece contact area of the cutting tool. A workpiece contact area can be a honed region of the cutting tool.

In other embodiments, a coating is subjected to a polishing post-coat treatment. Polishing can be administered with paste of appropriate diamond or ceramic grit size. Grit size of the paste, in some embodiments, ranges from 1 μm to 10 μm. In one embodiment, a 5-10 μm diamond grit paste is used to polish the coating. Further, grit paste can be applied to the CVD coating by any apparatus not inconsistent with the objectives of the present invention, such as brushes. In one embodiment, for example, a flat brush is used to apply grit paste to the CVD coating in a workpiece contact area of the cutting tool.

A coating described herein can be blasted or polished for a time period sufficient to achieve a desired surface roughness (R_(a)) and/or other parameters such as reducing residual tensile stress in the coating. In some embodiments, a coating subjected to post-coat treatment has a surface roughness (R_(a)) selected from Table III.

TABLE III Post-Coat Surface Roughness (R_(a)) Coating Surface Roughness (R_(a)) - nm ≦500 ≦250  <200 10-250 50-175 25-150 Coating surface roughness can be determined by optical profilometry using WYKO® NT-Series Optical Profilers commercially available from Veeco Instruments, Inc. of Plainview, N.Y.

Further, a post-coat treatment, in some embodiments, does not remove one or more outer layers of the coating. In some embodiments, for example, a post-coat treatment does not remove an outer layer of TiN, TiCN and/or TiOCN. Alternatively, a post-coat treatment can remove or partially remove one or more outer layers, such as TiN, TiCN and TiOCN.

II. Methods of Making Coated Cutting Tools

Methods of making coated cutting tools are also provided. A method of making a coated cutting tool described herein comprises providing a cutting tool substrate and depositing a coating by CVD over a surface of the cutting tool substrate.

Turning now to specific steps, a method described herein comprises providing a substrate. A substrate can comprise any substrate recited in Section I hereinabove. In some embodiments, for example, a substrate is cemented carbide, such as cemented tungsten carbide as described in Section I. Moreover, coatings deposited according to a methods described herein can have any construction and/or properties recited in Section I.

In some embodiments, one or more base layers of the coating reside between the substrate and the alumina containing layers. A base layer can comprise one or more metallic elements selected from the group consisting of aluminum and metallic elements of Groups IVB, VB and VIB of the Periodic Table and one or more non-metallic elements of Groups IIIA, IVA, VA and VIA of the Periodic Table. A base layer, for example, can be selected from the group consisting of titanium nitride (TiN), titanium carbonitride (TiCN) and titanium oxycarbonitride (TiOCN). In some embodiments, a multilayer arrangement is present comprising TiN and TiCN. General CVD deposition parameters for various base layers are provided in Table IV.

TABLE IV CVD Parameters for base layer deposition Pressure Duration Base Layer Composition Gas Mixture Temperature (° C.) (torr) (minutes) TiN H₂, N₂, TiCl₄ 800-900  60-300 20-120 TiCN(MT) H₂, N₂, TiCl₄, CH₃CN 750-900  30-300 60-300 TiCN(HT) H₂, N₂, TiCl₄, CH₄ 900-1050 30-300 30-200 TiOCN H₂, N₂, TiCl₄, CH₄, CO 900-1050 60-500 30-300

Additionally, methods described herein can further comprise depositing one or more outer layers over the alumina containing layer. An outer layer, in some embodiments, comprises one or more metallic elements selected from the group consisting of aluminum and metallic elements of Groups IVB, VB and VIB of the Periodic Table and one or more non-metallic elements selected from the group consisting of non-metallic elements of Groups IIIA, IVA, VA and VIA of the Periodic Table. In one embodiment, for example, an outer layer of TiCN and/or TiOCN is deposited with reference to CVD parameters set forth in Table IV. Coatings deposited according to methods described herein can have an architecture provided in Table IV above.

The alumina containing layers can be formed at the following example conditions: Temp: 800˜1500° C.; Pressure: 30˜500 torr; gas mixture of AlCl₃+H₂+CO₂+H₂S (optional)+HCl (optional) for 3˜600 minutes. The doped alumina can be formed at the following example conditions: Temp: 800˜1500° C.; Pressure: 30˜500 torr, gas mixture of AlCl₃+(TiCl₄ or ZrCl₄ or HfCl₄ or a combination thereof)+H₂+CO₂+H₂S (optional)+HCl (optional) for 1˜600 minutes and with different dopant introduction levels. CVD parameters pertaining to the alumina containing layers are provided in Table V.

TABLE V CVD Parameters for base layer deposition Pressure Duration Base Layer Composition Gas Mixture Temperature (° C.) (torr) (minutes) Al₂O₃ AlCl₃ + H₂ + CO₂ + H₂S 800-1500 30-500 3-600 (optional) + HCl (optional) MeAl₂O₃/MeO₂ [(AlCl₃ + TiCl₄ or ZrCl₄ or 800-1500 30-500 1-600 HfCl₄) or (their combination)] + H₂ + CO₂ + H₂S (optional) + HCl (optional)

In one embodiment of the present invention doping level is altered by controlling the ratio of Al/Me via the HCl gas flow introduced into the metal chloride generators. In another embodiment of the present invention, dopant introduction time is varied during the coating deposition. As well, it is possible to realize multi-periodicity of dopant-containing alumina and un-doped alumina sequences or different doping level sequences with different layer thickness ratios. Dopant introduction may be abrupt, ramped, variable, constant, high and low. Several embodiments of doping variations are shown in FIG. 7.

Further, the deposited coatings can be subjected to post-coat treatment(s) such as post-coat blasting or polishing as described in Section I hereinabove. Post coat blasting, in some embodiments, can change moderate tensile stress of the coating to moderate compressive stress or increase compressive stress in the as-deposited coating.

These and other embodiments are illustrated in the following non-limiting examples.

III. Examples Coated Cutting Tool

A coated cutting tool described herein was produced by placing a cemented tungsten carbide (WC—Co) cutting insert substrate [ANSI standard geometry CNMG432RN] into an axial flow hot-wall CVD reactor. The cutting insert comprised about 6 wt. % cobalt binder with the balance WC grains of size 1 to 5 μm. A coating having an architecture provided in Table VI was deposited on the cemented WC cutting insert according to the CVD process parameters provided in Tables IV-V. Al₂O₃—ZrAl₂O₃/ZrO₂ denotes a two layer system of α-Al₂O₃ and ZrAl₂O₃/ZrO₂. Samples A-D included the two layer system of α-Al₂O₃ and ZrAl₂O₃—ZrO₂. Sample E was included as comparative example and included only an α-Al₂O₃ outermost layer. All samples were initially coated with an outermost layers of TiCN/TiN. These layers were post-coat treated with a heavy wet blast of alumina particle slurry to remove the TiCN/TiN layers.

TABLE VI CVD Coating Architecture Sample Substrate CVD Coating Architecture n A WC—Co TiN*-TiCN(MT)-TiCN/TiOCN/[Al₂O₃/ 1 ZrAl₂O₃—ZrO₂]_(n) B WC—Co TiN*-TiCN(MT)-TiCN/TiOCN/[Al₂O₃/ 26 ZrAl₂O₃—ZrO₂]_(n) C WC—Co TiN*-TiCN(MT)-TiCN/TiOCN/[Al₂O₃/ 40 ZrAl₂O₃—ZrO₂]_(n) D WC—Co TiN*-TiCN(MT)-TiCN/TiOCN/[Al₂O₃/ 40 ZrAl₂O₃—ZrO₂]_(n) E WC—Co TiN*-TiCN(MT)-TiCN/TiOCN/Al₂O₃ — *Innermost layer adjacent to the substrate as a diffusion barrier. The resulting multilayered coating demonstrated the properties provided in Table VII. Deposition times were modified to produce the different layer thickness in A-D.

TABLE VII Properties of CVD Coatings A B C D E EXAMPLE (1X) (26X) (40X) (40X) (—) TiN 0.4 0.4 0.5 0.3 0.5 MT-TiCN 7.9 6.8 8.8 10.0 9.5 HT-TiCN/TiOCN 1.0 0.9 1.0 1.1 0.9 [Al₂O₃/ZrAl₂O₃—ZrO₂]_(n) 7.2 8.8 8.1 10.9 7.7 Total 16.2 16.9 18.3 22.3 18.5 Zr/Al ratio* 0.625 0.442 0.625 0.442 — ZrAl2O3 (μm) 7.2 0.17 0.08 0.10 —

IV. Metal Cutting Testing

Coated cutting inserts (A-D) and comparative coating insert (E) were subjected to continuous turning testing according to the parameters below. Two reps were performed to provide a mean tool life.

Workpiece—1045 Steel (C 45 DIN) Speed—1000 sfm

Feed Rate—304.8 m/min

Depth of Cut—0.08 mm Lead Angle: −5°

End of Life was registered by one or more failure modes of: Uniform Wear (UW) of 0.012 inches Max Wear (MW) of 0.012 inches Nose Wear (NW) of 0.012 inches Depth of Cut Notch Wear (DOCN) of 0.012 inches Trailing Edge Wear (TW) of 0.012 inches Three cutting inserts were tested for each coating architecture (1-4) providing repetition 1-3 data as well as mean cutting lifetime. The results of the continuous turning testing are provided in Table VIII.

TABLE VIII Continuous Turning Testing Results Repetition 1 Repetition 2 Coated Lifetime Lifetime Mean Cutting Cutting Insert (minutes) (minutes) Lifetime (minutes) A 5.6 8.5 7.1 B 14.7 15.0 14.9 C 14.0 13.7 13.9 D 13.2 13.8 13.5  E* 11.8 12.2 12.0 *Comparative Insert As provided in Table VIII, coated cutting inserts B-D having a multilayer structure of alternating doped and un-doped layers outlasted insert A with only one un-doped and doped layer and insert E having a continuous α-Al₂O₃ outer layer.

Various embodiments of the invention have been described in fulfillment of the various objects of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention. 

That which is claimed is:
 1. A coated cutting tool comprising: a substrate; and a coating comprising a plurality of alternating layers comprising a first layer of Al₂O₃ and a second layer of at least one of MeAl₂O₃ and MeAl₂O₃/MeO₂ composite; wherein Me is Zr, Hf, Ti or a combination thereof.
 2. The coated cutting tool of claim 1 wherein the MeO₂ is located within grain boundaries.
 3. The coated cutting tool of claim 1, wherein the first layer or second layer is 0.05˜0.5 microns thick.
 4. The coated cutting tool of claim 1, wherein the first layer and the second layer are each 0.05˜0.5 microns thick.
 5. The coated cutting tool of claim 1, wherein the first layer and the second layer are each less than or equal to 0.015 micron.
 6. The coated cutting tool of claim 1, the first layer comprises α-Al₂O₃, K—Al₂O₃ or a combination thereof.
 7. The coated cutting tool of claim 1, wherein the second layer is nearer the substrate than the first layer.
 8. The coated cutting tool of claim 1, wherein the first layer is nearer the substrate than the second layer.
 9. The coated cutting tool of claim 1, wherein the alternation of the first layer and second layer induces formation of a superlattice-like structure within individual grains of the coating.
 10. The coated cutting tool of claim 4, wherein an intervening layer between the substrate and the first layer comprises one or more metallic elements selected from the group consisting of aluminum and metallic elements of Groups IVB, VB and VIB of the Periodic Table and one or more non-metallic elements of Groups IIIA, IVA, VA and VIA of the Periodic Table.
 11. The coated cutting tool of claim 1, wherein the coating further comprises a base layer adjacent to the substrate surface.
 12. The coated cutting tool of claim 9 wherein the alternating coating layers have a chevron shape within a grain.
 13. The coated cutting tool of claim 9, wherein the base layer comprises at least one of TiN, MT-TiCN and TiOCN.
 14. The coated cutting tool of claim 1, wherein the coating further comprises an outermost layer comprising one or more metallic elements selected from the group consisting of aluminum and metallic elements of Groups IVB, VB and VIB of the Periodic Table and one or more non-metallic elements of Groups IIIA, IVA, VA and VIA of the Periodic Table.
 15. The coated cutting tool of claim 1, wherein the Me is present in weight % and the weight % varies between two or more second layers.
 16. The coated cutting tool of claim 1, wherein the Me is introduced and removed from a second layer in a gradient fashion.
 17. A method of making a coated cutting tool comprising: providing a cutting tool substrate; and depositing over a surface of the cutting tool substrate by CVD a coating comprising a plurality of alternating layers a first layer of Al₂O₃ and a second layer of at least one of MeAl₂O₃ and MeAl₂O₃/MeO₂ composite; wherein Me is Zr, Hf, Ti or a combination thereof.
 18. The method of claim 17, wherein the first layer or second layer is 0.05-0.5 microns thick.
 19. The method of claim 17, wherein the first layer is nearest the substrate.
 20. The method of claim 18, wherein an intervening layer is deposited between the substrate and the first layer, the intervening layer comprising one or more metallic elements selected from the group consisting of aluminum and metallic elements of Groups IVB, VB and VIB of the Periodic Table and one or more non-metallic elements of Groups IIIA, IVA, VA and VIA of the Periodic Table. 